The kind of front that usually forms long, thin stratus clouds is a warm front. Warm fronts involve warm air gradually sliding up and over cooler air, creating a broad, layered cloud cover including stratus clouds, which often appear as long, thin sheets. These clouds typically form ahead of the warm front and can thicken into altostratus or nimbostratus clouds with steady precipitation following.

Warm Front Characteristics

• Warm fronts feature warm, humid air rising over colder air, creating smooth, layered clouds.
• Stratus clouds formed are usually long and thin, representing the gentle lifting of air.
• These clouds signal the approach of a warm front and often precede more substantial clouds and precipitation.

Therefore, long, thin stratus clouds are typically associated with warm fronts.